1. Field of the Invention
The present invention generally relates to a method for forming a capacitor of a semiconductor device, and more specifically, to a method for forming of a capacitor wherein an etching barrier layer comprising a stacked structure of a nitride film and a tantalum oxide film is employed to prevent cracking and to provide sufficient support for storage electrode.
2. Description of the Prior Art
As the size of a cell decreases due to a high integration density of a semiconductor device, it becomes more difficult to obtain sufficient capacitance which is proportional to a surface area of a storage node.
In particular, in the DRAM wherein a unit cell includes a MOS transistor and a capacitor, a capacitance of the capacitor needs to be increased and an area occupied by the capacitor needs to be decreased to achieve high integration.
In order to increase capacitance C of a capacitor which follows the equation of (∈0×∈r×A)/T (∈0: vacuum dielectric constant, ∈r: dielectric constant of dielectric film, A: area of storage electrode, T: thickness of dielectric film), there are proposed methods of using a dielectric film having a high dielectric constant, of reducing the thickness of the dielectric film, or of increasing a surface area of a storage electrode.
A conventional method for forming a concave-type (or cylinder-type) capacitor (not shown) is as follows.
A device isolation film, an impurity junction region, a word line, a bit line and a contact plug for storage electrode are formed on a semiconductor substrate. Then, an interlayer insulating film is formed on the resulting structure.
A nitride film having a thickness of less than 1000 Å, which is an etching barrier layer, is formed on the resulting structure.
An oxide film for storage electrode is formed on the nitride film. The oxide film has a thickness of more than 15000 Å and consists of BPSG, PSG or TEOS.
Thereafter, the oxide film for storage electrode is etched via a photolithogrphy process using a storage electrode mask to form a storage electrode region exposing the storage electrode contact plug.
A conductive layer for storage electrode connected to the storage electrode contact plug is formed on the entire surface of resulting structure including the storage electrode region.
Next, a photoresist film filling the storage electrode region is formed on the entire surface of the resulting structure, and then planarized to expose the oxide film for storage electrode.
Thereafter, the photoresist film is removed so that only a portion of the conductive layer for storage electrode on the surface of the storage electrode region remains. The oxide film for storage electrode is then removed to form a concave-type storage electrode. The process of removing the oxide film for storage electrode is performed using BOE solution. The nitride film, which serves as an etching barrier layer, is damaged during the process.
A dielectric film is formed on the surface of the storage electrode, and an annealing process then is performed. The annealing process is performed under an oxygen atmosphere at a temperature higher than 700° C. During the annealing process, cracks are generated in the damaged nitride film, and thus the nitride film cannot support the storage electrode. As a result, the storage electrode collapses, which leads to bridging between adjacent storage electrodes. Moreover, oxygen atoms penetrate through the cracks to oxidize a lower bit line.
A plate electrode is then formed to complete the formation of a capacitor.
FIG. 1a is a photograph showing a cross-section of a conventional capacitor of a semiconductor device wherein the lower bit line is oxidized by the oxygen atoms.
FIG. 1b is a plane view illustrating the structure of the conventional capacitor shown in FIG. 1a. 
FIG. 2 is a photograph showing a plane view of the conventional capacitor of a semiconductor device wherein bridging between adjacent storage electrodes due to lack of support by the etching barrier layer are shown.
As described above, according to the conventional method for forming a capacitor device, the nitride film serving as an etching barrier layer is damaged in the process of removing the oxide film for storage electrode. This damage causes bridging between adjacent storage electrodes. Moreover, cracks in the etching barrier layer generated during the annealing process causes oxidation of lower conductive layers due to oxygen atoms penetrating through the crack.
As a result, characteristics and reliability of semiconductor device are degraded, and high integration of the semiconductor device cannot be achieved.